A significantly large amount of study has been conducted for network apparatuses. The most popular one is a network apparatus using IP (Internet Protocol) network. In addition, MPLS (Multi Protocol Label Switching) aiming at accommodating a plurality of protocols and networks is a technique related to a network apparatus that has a mechanism to automatically generate a path. Meanwhile, typical examples of ad-hoc algorithm include AODV (Ad-hoc On-Demand Vector) and OLSR (Optimized Link State Routing).
In an IP network apparatus, routing for a packet is performed according to the IP address. The IP address has a tree structure. Therefore, through procedures as described below, a packet can be transmitted to a terminal being the final target. That is, sequentially from the higher octet of the destination IP address of the packet, search for a network apparatus managing the IP network corresponding to the IP address that matches with the destination IP address by prefix search, and transmission of the packet to the detected network apparatus are repeated.
Routing is determined according to the IP address scheme. A routing table defines which network apparatus manages which IP network. While the routing table is often set manually, it may be updated automatically by RIP (Routing Information Protocol). RIP is a system in which network apparatuses broadcast the IP networks they manage to their surroundings, for the network apparatuses to check with each other the IP networks they manage.
In MPLS, the network is separated into an internal network being a network between network apparatuses called LSR (Label Switch Router), and an external network. A frame from the external network is taken into the internal network by an apparatus called an edge node (that is, a network apparatus that straddle both the external network and the internal network).
At this time, a label is inserted to the head of the external frame. Each LSR has a label forwarding table. The label forwarding table holds the label of the input frame and the label and destination of the output frame. LSR takes out the label of an input frame, finds the corresponding label from the label forwarding table, changes to the label of the output frame, and sends out to the corresponding destination.
The process described above is performed by LDP (Label Distribution Protocol) in the label forwarding table. LDP is a protocol in which generation of a routing table by RIP and the like is performed first, a label is added to it, and notification between adjacent nodes is performed.
AODV is a method in which, using broadcast for path search, other communication node apparatuses repeat broadcasting to find the path to the target node apparatus. The communication apparatus transmits a frame called “Route Request (RREQ)” to its surroundings to find the target path. The frame clearly states the communication node ID of the search target.
Communication node apparatus in the surrounding generate, when themselves are not being searched, a new RREQ frame and repeat broadcasting to their surroundings. At this time, each communication node apparatus records from which adjacent node apparatus the message of the transmission source was received. When the RREQ message reaches the target communication node apparatus, the target communication node apparatus generates “Route Reply (RREP)” frame, and transmits the RREP frame so that it follows the path through which the RREQ frame was transmitted. As described above, a bidirectional communication path is created.
In OLSR (Optimized Link State Routing), a system is adopted in which communication node apparatuses exchange frames with each other regularly, to understand the entire network and to detect the path to the target communication node. Communication node apparatuses send out HELLO frames periodically, to send notification of existence to each other. When the existence of the communication node apparatus to be the communication partner is identified, a path for flooding to distribute a frame to the entire network efficiently is generated. This is called MPR (Multi Point Relay).
According to MPR, frames may be broadcasted to the entire network efficiently from each communication node apparatus. Next, node apparatuses distribute TC (Topology Control) frames being a path generation message to each other using the MPR, all the node apparatuses may know the network topology.
In order to send a frame to a target communication node apparatus, the communication node apparatus to be the transmission source refers to the network topology that itself knows, and hands over the node to the adjacent communication node apparatus to which it should be sent. The adjacent node apparatus performs the process similarly, and the frame is delivered to the target node apparatus eventually.
Regarding the ad-hoc wireless communication network, for example, the following technique has also been disclosed. That is, each node broadcasts information as notification of the existence of own node as a HELLO message, and information including the route metric to own node. Then, another node that received the HELLO message adds, to the received route metric, the route metric for the route between the node that has broadcast the HELLO message and own node, and uses the route metric after the addition. The route metric here is a value indicating the cost for the transmission source and the destination calculated by factors such as the number of hops, link quality, and so on.
The technologies described in the following documents are well known.
Document 1:
    Japanese National Publication of International Patent Application No. 2006-526937Document 2:    Japanese Laid-open Patent Publication No. 2003-273964Document 3:    Japanese Laid-open Patent Publication No. 2002-271399Document 4:    Japanese Laid-open Patent Publication No. 2006-340165Document 5:    Japanese Laid-open Patent Publication No. 2001-298488Document 6:    Japanese Laid-open Patent Publication No. 2006-33275Document 7:    Japan Patent No. 4173842Document 8:    Tadashige IWAO, Kenji YAMADA, Koji NOMURA, Takeshi HOSOKAWA. “Multipurpose Practical Sensor Network: S-wire”. FUJITSU magazine, May 2006 (VOL. 57, NO. 3), pp. 285-290.
As described above, while a large amount of studies have been conducted for network techniques, there has been a following problem for various network systems that assume that each node apparatus within the network recognizes the network topology. That is, since the network environment may change dynamically, even if anode apparatus attempts to transmit data in a data transmission phase based on the network topology recognized in advance in the path generation phase, the transmission is not necessarily successful.